One result of a fast booming economy in an urban area is that the population and the numbers of vehicles increase quickly. Further, many high buildings are also built in rapid succession. A conventional parking lot is normally not fully capable of handling the increased demand for vehicle parking space. Consequently, an uncontrolled parking state occurs: in a slow lane, in a lane of a street, and on a sidewalk. Thus traffic jam, arrive with vehicles and pedestrians are inconvenienced, especially during the so-called rush hours. The traffic jam condition not only jeopardizes traffic safety in a city but also impedes the control of traffic.
FIGS. 13 to 17 illustrates the prior art design of an elevator for moving a car. An associated hoist, while moving forward, generates a force F to drive the respective platform forward. The balance or equilibrium of the platform and the car thereon can be calculated with the following two formulae.
The sectional view A--A of FIG. 17 shows the backward movement of the platform subject to the force F.
______________________________________ F (X) = Ma F = Ma = Wa/g (1) To = 0 Ws - FH cos.theta. = 0 (2) s = Hsin.theta. Solving (1) and (2), one gets a/g = Tan0.1 Let: a = g/10 Tan.theta. = 0.1 .theta. = 5.degree.43' h = H - Hcos.theta. = H (1 - Cos.theta.) = .00497 H s = Hsin.theta. = .0996 H ______________________________________
The above values for O, h and s are based on the assumption of a=g/10. They are of considerable magnitude. In actual design, four rods are fixed to respective corners of the hoist and fixed at A and B to form a cantilever beam to resist the force F so that there is a bending stress on A by the torque of M=FH=WH a/g. Material at A tends to be subjected to fatigue stress and may fracture since its both sides are subjected alternatively to respective force. Therefore, in order to extend the service life, the values of a, H and W must be minimized to minimize the stress at A.
The smaller the value of a is, the greater will be the time required for parking and unloading; the a smaller value for H will increase the construction cost a smaller value of H will lead to a reduced capacity of the cage.